Process of modifying the characteristics of pigments, and product



Patented Jan. 10, 1933 UNITED STATES PATENT OFFICE HENRY A. GARDNER, WASHINGTON, DISTRICT 01' COLUMBIA PROCESS OF MODIFYING TEE CHARACTERISTICS OF PIGHENTS, AND PRODUCT Ra Drawing.

The resent invention relates to the treatment 0 pigments, and particularly of titanium-base pigments, whereby to improve or modify properties thereof: it relates, also,

5 to the products obtained as a result of such treatment.

It is known that when the commercial titanium pigments now produced are ground in varnish liquids, and especially in tung oil varnishes which are highly polymerized and which may contain rosm esters, phenolformaldehyde-rosin esters, glycerin phthalate resins, and/or similar resins, aging may sometimes cause either a stiifening of the product or 'a settling out of some of the solids, sometimes in the form of a hard cake. However, the greatest drawback of known paints made with titanium pigments is the pronounced chalkinglwhich they shown when 0 exposed to the weat er. Thus, for instance, when these pigments in the form of paints are exposed on wooden surfaces for a period of less than a year, pronounced chalking and washing may occasionally take place to such 5 an extent that the wood is disclosed in many places. This makes it necessary at the present time to use in the paints, high percentages of zinc oxide, white lead, or other pigments with these titanium pigments in order to se-' a cure durable results. Since the hiding power of zinc oxide or white lead is much lower than that of titanium pigments when ground in oil it can be appreclated that pamts of a comparatively lower hiding power are produced.

An object of the present invention is to provide titanium-base pigments having materially reduced chalking tendencies. An-

other object of invention is to provide titanium-base pigments which when ground into a paint in varnish liquids such as a tung oil varnish show improved suspendability in the paint with decreased settling out.

The above and other objects of invention are attained by carrying out a process which consists essentially in enveloping the particles of titanium-base pigment with a film covering of a water-insoluble inorganic or organic compound. By the expressions titanium-base pigment, or simply titanium Application filed January 22, 1981. Serial No. 510,585.

pigment, used therein, I mean to include plgments containing a substantial proport1on of a titanium compound having pigmenting properties: I refer specifically to titanium oxide and to titanium oxide coalesced with barium sulphate, calcium sulphate, or a similar product. Pigments of this character are described in the patent disclosures of Barton and Rossi. Said pigments, in the forms in which they normally 00 occur in commerce, may and usually'do contam, in small amounts, acidic constituents, iron sulphate and/or titanium sulphate, or their products, as impurities.

In carrying out this process I may treat the titanium pigment suspended in a liquid vehicle, which may be water, with a small but eifective amount of chemicals which will produce upon the surface of the titanium pigment a water-insoluble compound; or, I may coat the particles with a pre-formed water insoluble substance in liquid state. Among the inorganic products with which I have experimented in this relation are: zinc phosphate, lead phosphate, barium selenide, silver carbonate, zirconium oxide, tin carbonate, zinc vanadate, lead tungstate and sulphur. Thus, in coating the particles with an inorganic compound 100 grams of the titanium pigment are suspended in water and sufficient appropriate chemical solutions are added to the water suspension to interact to the formation of a water-insoluble compound such as one of those above named, whereby there will be precipitated upon the surface of the inert titanium pigment about 5% of the said compound. In accordance therewith, to the aqueous suspension of 100 grams of the titanium pigment, e. g., ordinary commercial titanium oxide or the titanium oxide-barium sulphate pigment known by the name Titanox, I may, add a sodium salt of selenium v and, thereafter, barium chloride, in amounts suflicient to produce insoluble barium selenide, with the result that the particles of the titanium pigment become coated with a film of the said barium selenide. Or, I may dissolve oxalic acid in water, suspend the titanium pigment therein, and thereafter add a suitable quantity of a water-soluble metallic salt capable of reacting with the oxalic acid to the formation of a water-insoluble oxalate, say lead acetate, thus producing lead oxalate.

Other or anic compounds which I have utilized for this pur ose include rubber latex which is precipita le on the surfaces of the particlesbyaddin traces of acid. Ihavealso ex rimented wit rubber dispersions in benzo which are precipitable by drying the pigment which is suspended in the rubber-benzol mixture. I have also experimented with ammoniated casein solutions which are precipitable upon the titanium pigment by mere heating or by the addition of traces of acid.

A preferred procedure, however, is to use an alkali metal salt of a soap-forming acid.

Among the soap-forming acids which are suitable are tung oil acids, linseed oil acids, stearic acid, ordinary rosin acids, and the acids from synthetic resins.

The invention will be described in great particularity in regard to the following specific examples:

Example 1 no longer objectionable. These products,.

which are really responsible for many of the defects in titanium pigments as now produced, are thus removed from reaction. The mass is further heated for a period of five minutes, and there is then added sufficient zinc chloride, zinc sulphate, or other watersoluble zinc salt to precipitate any unacted upon portion of the Ivory soap, thus producing zinc oleate or zinc stearate which coats over the particles of pigment. The resulting product thereafter is filtered, washed and dried.

In place of the Ivory soap referred to above, I may use an equal quantity of sodium resinate roduced by saponification of the alkali with ordinary rosin. The reaction proceeds in the same direction and a similar product is produced. In place of the titanium oxide I may similarly treat titaniumbarium pigment, or titanium-calcium pigment.

The pigment product produced by the carrying out of the above process has a lower oil absorption than the pigment previous to treatment. This is due apparently to the washing out of the impurities in the titanium pigment or reaction therewith period of time without show any pronounced settling or hardening. t also produces a paint which when ex out of doors will not show nearly so much chalking for a period up to one year, as compared to a paint made with ordinary titanium pigment.

I have, for instance, made accelerated tests of paints produced with such pigments as compared to the pigments before treatment. These tests were made with alternate exposure to ultra-violet light from a quartz tube mercury vapor are lam and water spray in a specially designed ca inet. In this test, paints made with the ordina I pigments would chalk heavily in a period 0 three days time, whereas the treated pigments would not show any marked chalking or disruption of the film after a period of eleven days. This period of eleven days may possibly be the equivalent of actual outdoor ex ure for a period of eighteen months. remarkable weathering obtained by pigments so treated with soaps is probably due to the extra resistance which these pigments have to wetting. For instance, the dry pigments after production will repel water in a manner heretofore unknown with res to titanium pigments. This may be i ustrated when small samples of in product are dropped into water. The partic es do not sink immediately to the bottom but form spherical globular masses which seem to be coated with air bubbles. This phenomenon is a distinguish? characteristic of pigments treated in acco anee with lnay process.

In rega to the oil absorption of these pigments, I wish to state that this treatment is quite remarkable in that it eflects a reduction of the'oil absorption to a very great extent. Thus, for instance, if 100 pounds of a titanium-barium pigment requires 16 pounds oflinseed oil to thoroughl wet the surface and make a stifi paste, as ow as 12 pounds of oil is suflicient therefor after the pigment has been coated over with zinc stearate or similar stearate according to my process. While much of this reduction of oil absorption is due to the presence of the stearated surface, it is also probable that the boiling treatment produces aggregation of the part1- cles, which makes the pigment uire less oil. The washing out or neutralization of the iron or titanium sulfates in thepi ent also allows of a quick wetting with o' ia o 10 with what appears to be calcium stearate or other metallic stearate.

Ewarmple 2 I heat 100 ams of calcium Titanox and 200 grams water which contains grams of Ivory soap. Within two or three minutes the soap 1s entirely taken out of solution and precipitated on the calcium Titanox in an insoluble metallic soap form.

No zinc sulphate or other reagent is required to precipitate. The pigment thus produced is quite remarkable in its properties. It is extremely white. It repels water tremendously. This makes it possible to use this pigment for outside paint, a place where it has heretofore been unused to any extent because of its slightly water soluble properties which cause the paint to chalk ofi quickly.

A similar improvement of titanium-base pigment is effected by deposition .on the particles thereof of a water-insoluble inorganic compound such as those hereinbefore noted.

In place of the soaps and/or inorganic compounds to which I have previously referred, I may coat over the particles of a titanium pigment with beta elaeostearin which will form during the coating process. Beta elzeostearin is produced from ordinary tung oil by the effect of light. This product is described in Circular No. 256, Henry A. Gard ner and H. C. Parks, Scientific Division, Educational Bureau, Paint Manufacturers Association of the U. S., 1925. It has unique properties in that after being formed and dried, it becomes insoluble in oil and practically all solvents. By the following process I successfully coat the particles of pigment with this material in order to waterproof them and obtain a waterproofing that is highly insoluble.

Example 3 100 grams of tung oil (China-wood oil) are placed in a container, and there is added thereto a trace ofsulphur or iodine. Usually 0.1% is suflicient. This tung oil is placed under strong light, such as the irradiation from carbon arcs or mercury quartz tubes, for a period of twenty minutes. During this period beta elaeostearin is induced. The oil is still clear, but if it were allowed to cool it would become aslid white mass as stiff as wax. This phenomenon is due to the large quantity of beta elaeostearin which has been formed in the oil by the action of the light.

Before theoil is allowed to cool, I add it, drop by drop, to 2000 grams of Titanox which is constantl being stirred in a mechanical device. P thls method the oil coats over the partic es of pigment to a very great extent. The pigment is then spread out on pa er and allowed to dry for a period of a few ours, during which time the beta claeostearin becomes solid and insoluble.

In order to make the coating-over process, as outlined above, more perfect, I may dissolve the grams of the so-treated tung oil product consisting essentially of beta elaeostearin in 100 grams or more of a solvent such as acetone, in which it is soluble while hot and just after its treatment. This allows the tung oil roduct to be spread over a greater areao pigment. Darin the mixing operation the acetone or other so vent evaporates, leaving a very thin film of the tung oil product on the pi ent.

The pigment t us produced is highly waterproof. It has a lower oil absorption than the original pigment. The pigment and its coating are insoluble in oil and other ordinary solvents for oil. When made into a paint, this pigment has very great durability, and does not require zinc, lead, or other pigments to prevent rapid chalking.

I have discovered, also, that this use of beta ela-iostearin is not restricted to titaniumbase pigments, but includes all dry pigments, whether white or colored, of any composition whatsoever. I have found that the waterproofness of a dry pigment may be improved and that its oil absorption ratio may be lowered by coating the particles thereof with beta elaeostearin in either of the manners above described with relation to a titaniumbase pigment. Included in the class dry I pigments I may mention white lead carbonate or sulphate, lithopone and other zinc sulphide pigments, zinc oxide, natural iron earth pigments such as ochre and sienna, and all chemically precipitated or manufactured pigments such as Prussian blue, Para red, lead chromes, and the like.

I claim:

1. Process which comprises coating the surfaces of particles of a pigment with a filmcoating of beta-elaeostearin.

2. As a new product, a white pigment comprising a titanium compound having pigmenting properties, the particles of which pigment are coated with beta-elaeostearin.

3. Process which comprises adding a dry pigment, by portions and with thorough mixing, to a liquefied organic mixture consisting essentially of beta-elaeostearin.

4. Process which comprises adding a dry pigment, by portions and with thorough mixing, to a solution of beta-elaeostearin in a suitable volatile organic solvent therefor, and removing the solvent.

5. As a new product, the pigment product obtained by the carrying out of the process defined in claim 3.- r

6. As a new product, the pigment product obtained by the carrying out of the process 5 defined in slaim 4.

Tn testimony whereof, I aflix my signature.

HENRY A. GARDNEE.

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